Vertical Surface: Using a Tip 3 (or any small round tip), hold the bag at an angle and touch the tip to the surface.
Squeeze, drawing the icing on the surface (this step is the same for vertical, horizontal and curved lines)
To end the line, stop squeezing and pull away.
Flat surface: Hold the bag at an angle and touch the tip to the surface. Squeeze a small amount of icing to attach the starting point to the surface.
Lift the tip slightly as you squeeze, letting the line of icing drop into place. Guide the placement of the line as the icing squeezes out of the tip. (this step is the same for vertical, horizontal and curved lines)
Push the tip back to the surface to finish the line. Stop squeezing and pull away.
Piping lines are foundation of many decorating techniques, such as piping a lattice
While lines are usually piped with a round tip, try using a star tip or a basketweave tip to create different widths and texture.